Report on Poas (Costa Rica) — July 1985

Scientific Event Alert Network Bulletin, vol. 10, no. 7 (July 1985)
Managing Editor: Lindsay McClelland.

Poas (Costa Rica) Fumarole temperatures drop

Please cite this report as:

Global Volcanism Program, 1985. Report on Poas (Costa Rica). In: McClelland, L (ed.), Scientific Event Alert Network Bulletin, 10:7. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.SEAN198507-345040.

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Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2708 m

All times are local (unless otherwise noted)


Activity was characterized by the emission of gas from fumaroles on the eroded 1953-55 cone. Fumarole temperatures continued to drop, while crater lake temperature remained constant (table 3).

Table 3. Temperatures (in °C) measured in a fissure on the E side of the eroded 1953-55 cone and in the crater lake, January 1982-October 1985.

[Skip text table]
    Date        Fumarole     Crater Lake   Lake Water
               Temperature   Temperature       pH

    Jan 1982      860            47           --
    Feb 1982      883            48           --
    Mar 1982      887            47           --
    Apr 1982      873            50           --
    Dec 1982      731            40           --

    Jan 1983      753            56           --
    Feb 1983      732            60           --
    Mar 1983      780            60           --
    Apr 1983      818            60           --
    May 1983      832            57           0.06
    Jun 1983      834            57           0.1
    Jul 1983      822            57           0.2
    Aug 1983      806            58           0.2
    Sep 1983      810            58           0.3
    Oct 1983      801            60           0.6
    Nov 1983      750            58           --
    Dec 1983      750            56           0.07

    Jan 1984      690            51           0.7
    Feb 1984      650            51           --
    Mar 1984      570            54           0.7
    Apr 1984      570            49           --
    May 1984      586            50           --
    Jun 1984      603            50           --
    Jul 1984      602            48           --
    Aug 1984      530            48           --
    Sep 1984      500            50           --
    Oct 1984      490            48           --
    Nov 1984      510            48           --
    Dec 1984      515            48           --

    Jan 1985      550            44           --
    Feb 1985      560            44           --
    Mar 1985      584            44           --
    Apr 1985      568            44           --
    May 1985      490            44           --
    Jun 1985      420            48           --
    Jul 1985      316            46           --
    Aug 1985      295            45           --
    Sep 1985      294            45           --
    Oct 1985      310            45           --

Geologic Background. The broad, well-vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano, which is one of Costa Rica's most prominent natural landmarks, are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the 2708-m-high complex stratovolcano extends to the lower northern flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, is cold and clear and last erupted about 7500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world's most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since the first historical eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.

Information Contacts: J. Barquero H. and E. Fernández S., Univ. Nacional, Heredia.